The present invention relates to a boost converter as a boost switching regulator or a boost chopper circuit. More specifically, the invention relates to a technology effectively applicable to a semiconductor integrated circuit having a DC-DC boost converter.
A boost converter as a boost chopper circuit supplies an electric current from an inductor to a first MOS transistor to accumulate an energy in the inductor. The boost converter supplies an electric current to a second MOS transistor from the inductor where the energy is accumulated. By repeating this operation, the boost converter is supplied with a boost voltage at an output terminal coupled to a smoothing capacitor. According to its characteristic, the boost converter causes an input terminal voltage lower than an output terminal voltage during a boost operation that complementarily controls the first and second MOS transistors. The input terminal is coupled to the inductor and is supplied with an electric current. By contrast, a higher voltage is applied to the input terminal in a boost disabling state that turns off the first and second MOS transistors. That is, the boost operation and the boost disabling state reverse a source/drain structure of the second MOS transistor. Japanese patent laid-open Nos. 1996-251913, 2005-253254, and 2005-295629 describe the technologies of using a switch to couple a back gate (substrate) of the second MOS transistor to the input or output terminal depending on the boost operation or the boost disabling state. During the boost operation, the technologies prevent an electric current from leaking from the output terminal to the input terminal due to a parasitic diode of the second MOS transistor. During the boost disabling state, the technologies prevent an electric current from leaking from the input terminal to the output terminal due to a parasitic diode of the second MOS transistor.